/Engine/Source/Runtime/Engine/Public/MaterialCompiler.h
virtual int32 StrataHorizontalMixingParameterBlending ( int32 Background, int32 Foreground, int32 HorizontalMixCodeChunk, int32 NormalMixCodeChunk, const [FString](API\Runtime\Core\Containers\FString) & SharedLocalBasisIndexMacro, [FStrataOperator](API\Runtime\Engine\Rendering\FStrataOperator) * PromoteToOperator )